发布数据时，我认为模式有一个构造函数不工作 [英] Posting data when my view model has a constructor does not work

问题描述

我有以下的code：

[HttpGet]
public ActionResult Edit(int req)
{
    var viewModel = new  EditViewModel();
    viewModel.RequestId = int;
    return View(viewModel);
}

[HttpPost]
Public ActionResult Edit(EditViewModel viewModel)
{
// some code here...
}

它正常工作：当编辑表单发布，我有动作控制器谁是所谓

It works fine: when the edit form is posted, I have the action controller who is called.

现在我修改一些点点我的code是这样的：

Now I modify some little bit my code like this:

[HttpGet]
public ActionResult Edit(int req)
{
    var viewModel = new  EditViewModel(req);
    return View(viewModel);
}

[HttpPost]
Public ActionResult Edit(EditViewModel viewModel)
{
// some code here...
}

public class EditViewModel()
{
    public EditViewModel(int req)
    {
        requestId = req; 
    }
    ...
}

在这个新版本中，我有一个构造器视图模型。

In this new version, I have a view model with a contructor.

这一次，当我的窗体回，动作控制器永远不会触发。

This time, when my form is posted back, the action controller is never triggered.

任何想法？

感谢。

推荐答案

这是正常的。默认的模型绑定不再实例化视图模式，因为它没有一个参数的构造函数。您必须编写自定义模型绑定，如果你想使用没有默认构造函数视图模型。

That's normal. The default model binder can no longer instantiate your view model as it doesn't have a parameterless constructor. You will have to write a custom model binder if you want to use view models that don't have a default constructor.

通常你不需要这样的自定义构造函数。你可以简单地有像你的视图模型：

Normally you don't need such custom constructor. You could simply have your view model like that:

public class EditViewModel()
{
    public int RequestId { get; set; }
}

和POST操作这样的：

and the POST action like that:

[HttpPost]
public ActionResult Edit(EditViewModel viewModel)
{
    // some code here...
}

现在你需要做的就是POST的的requestId 参数，而不是 REQ 键，默认模式粘结剂将做这项工作。

and now all you have to do is POST the requestId parameter instead of req and the default model binder will do the job.

如果因为某些原因，你想使用自定义构造一个视图模型，这里的自定义模型粘合剂如何可能看起来像一个例子：

And if for some reason you wanted to use a view model with custom constructor, here's an example of how the custom model binder might look like:

public class EditViewModelBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        var req = bindingContext.ValueProvider.GetValue("req");
        if (req == null)
        {
            throw new Exception("missing req parameter");
        }
        int reqValue;
        if (!int.TryParse(req.AttemptedValue, out reqValue))
        {
            throw new Exception(string.Format("The req parameter contains an invalid value: {0}", req.AttemptedValue));
        }

        return new EditViewModel(reqValue);
    }
}

这将在注册

您的Application_Start ：

ModelBinders.Binders.Add(typeof(EditViewModel), new EditViewModelBinder());

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